The present invention relates to a disposable diaper, more particularly to a disposable diaper formed in pants type.
It is well known for disposable diapers formed in pants type comprising heat-weldable top- and backsheets to seal front and rear bodies to each other by means of heat welding along transversely opposite sides of front and rear waist sections. For example, Japanese Laid-Open Patent Application No. 1993-15551, of which the applicant is the same as the applicant of the present application, discloses a sealing technique for pants type diapers, by which a series of intermittent rectangular welded zones each having a long side extending in parallel to a waist line of the diaper are longitudinally arranged along each lateral side of the front and rear waist sections utilizing an ultrasonic welding. Use of this technique enables the diaper put on a wearer to be easily stripped off merely tearing off the diaper along the sealed side edges of the diaper. This technique is advantageous also in that the interior of the diaper is always maintained in good communication with the exterior of the diaper and thereby the diaper of high air-permeability is obtained.
Tearing off tends to take place along a peripheral edge of each welded zone as the diaper is torn off. The sheets usually used to form the diaper comprise a thin nonwoven fabric or a plastic film of a relatively small weight per unit area and a correspondingly low tear strength, since, after the sheets have been welded to each other, the welded zone exhibits a tear strength higher than that exhibited by the nonwelded zone and a tearing force is concentrated along a boundary between the welded zone and the nonwelded zone. Consequently, there is an apprehension that a tear might progress circumferentially, i.e., transversely into the front and/or rear bodies as the diaper is torn off along the long side of each rectangular welded zone, instead of being torn longitudinally of the diaper. Such undesirable phenomenon will readily occur particularly when both the top- and backsheets exhibit a lower tear strength in transverse direction significantly than a tear strength in longitudinal direction. Unless the diaper is torn off in the longitudinal direction, it will be impossible to relieve the wearer from the diaper as quickly as possible.
Accordingly, a principal object of the invention to solve the problem as has been mentioned above by providing a diaper with welded zones at least partially defined by patterns each having contours diverging transversely of the diaper so that the diaper may be easily torn off along such contours obliquely downwards.